466 THE SMALL GRAINS 



The underground stems send up new shoots each spring, 

 which are avoided by all stock, if possible. The weed is 

 more common on upland soil. The stems are yielding to 

 implements, and therefore often escape being cut. Im- 

 plements having V-shaped knives or broad-edged cutting 

 tools, around which the stems cannot glance, should be 

 employed in eradication. Growing an intertilled crop 

 will be of great advantage. 



509. Perennial sow thistle (Sonchus arvensis, Linn.) 

 is called one of the worst weeds in Minnesota. It is 

 common in waste places, along roadsides, and in culti- 

 vated fields, from the Atlantic Coast to the Great Plains, 

 both in this country and Canada. The seeds seldom occur 

 in commercial grain. 



The bright yellow flowers of perennial sow thistle are clustered 

 in heads, from 1 to 2 inches across. The oblong dark brown seeds 

 are longitudinally ribbed on the surface, and when mature, they have 

 a dense tuft of hairs attached, which aids in then* distribution by the 

 wind (Fig. 142 /). 



The first stray plants should be cut out individually. 

 Badly infested fields may have to be fallowed, or be 

 planted with an intertilled crop. A short rotation may 

 well be practiced, such as (1) grain, (2) clover, and (3) a 

 cultivated crop. l 



The common and prickly sow thistles (S. oleraceus, 

 Linn., and S. asper, Hill), both annuals, are often bad 

 weeds. 



510. Wild rose (Rosa spp.). There are several species 

 of wild or prairie rose that are troublesome in grain fields, 

 particularly in the Prairie states and the Prairie provinces 

 of Canada. The seeds are often found in the thrashed 

 grain of wheat and oats. 



